<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<script src="https://apps.bdimg.com/libs/jquery/2.1.4/jquery.min.js"></script>
	</head>
	<body>
		<div>
			<p>这是第一个段落</p>
		</div>
		<div>
			<p>这是第二个段落</p>
		</div>
		<div>
			<p>这是第三个段落</p>
		</div>
		<script type="text/javascript">
			$(function(){
				$("p").first().css("background-color","yellow")
			})
		</script>
	</body>
</html>
